When performing various machining operations, especially machine operations on a drill press, is it frequently necessary to determine the precise center of a workpiece which is being worked upon. There have been several prior proposals for techniques for determining the center. One of these techniques employs the use of a gauge which conventionally is connected to a jointed arm which arm in turn can be chucked into the chuck jaws of a drill press or similar machine. The gauge is secured by some type of clamping means on the end of the jointed arm and the jointed arm is then extended in some manner to bring the gauge into contact with the workpiece.
The workpiece to be centered will be provided with some type of cylindrical surface which is either an interior or an exterior surface, and the gauge is engaged against this surface while the chuck is rotated with the gauge being continuously held in contact with the cylindrical surface. The fluctuation of the gauge during this rotation of the chuck jaw will indicate how much offcenter the piece is and in which direction. A skilled machinist looking at the gauge, will then be able to reposition the workpiece and again take the readings from the gauge, with this repositioning taking place several successive times if necessary, until the gauge shows no deviation of the cylindrical surface from the center. When the gauge ceases fluctuation during rotation, this will then indicate that the workpiece is centered precisely in the center of the cylindrical surface which has been used as the reference.
While this technique is an effective way for determining the center, nevertheless the conventional prior fixtures or arms for mounting the gauge have demonstrated certain limitations. Specifically, the mounting arms have to provide the needed extension and flexibility for the gauges to be able to contact surfaces which may be a great distance away from the chuck jaws, either laterally or vertically, so these are for centering on pieces where the cylindrical surface is relatively near the chuck. Also the prior gauge holders have not proved to be effective in many cases to access difficultly placed or hard to reach surfaces, the centers of which are to be determined.